This paper showed results from one of the cross-arc lines in the Aleutians (A1), based on reflection and OBS data (Fig. 1 at right). The results showed that the average velocity structure of the arc on Line A1 was too fast to represent a bulk andesitic composition and was significantly faster (and thus more mafic) than mature continental crust (Fig. 2 at right).
You can download a PDF of the paper here.